Homotypic and heterotypic IgG and IgM antibody responses in adults infected with small round structured viruses

Antibody responses to recombinant Norwalk (rNV) and Mexico (rMXV) viral capsid proteins were studied in 39 adults involved in outbreaks of gastroenteritis associated with genogroup 2 small round structured viruses (SRSVs). Nineteen individuals were involved in outbreaks associated with MXV-like strains and 20 in outbreaks associated with four other genogroup 2 SRSVs. IgG antibodies were measured in acute and convalescent sera using indirect enzyme-linked immunosorbent assay (ELISA), and IgM was measured by indirect and capture ELISAs. Nineteen (49%) patients demonstrated a significant rise in IgG to rMXV with four (10%) patients also showing anamnestic responses to rNV. Fourteen patients were positive in the rMXV IgM-capture ELISA, representing 74% of patients demonstrating IgG rises. IgG and IgM responses to rMXV were observed in both groups, although higher levels of responses were seen in adults infected with MXV-like strains than those infected with non-MXV genogroup 2 viruses. No significant IgM responses were observed to rNV. These results indicate that, following SRSV infection, adults show a rise in antibody which is broadly reactive to viruses within but not between genogroups, although greater homotypic than heterotypic responses are produced. These findings have implications for interpretation of seroepidemiological studies and serodiagnosis of SRSV infections using recombinant capsids.